Download Hybrid Static/Dynamic Activity Analysis*

Normalized Execution Time
2
1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
No Activity Check
Pure Dynamic (1.39)
May w/o Dyn (0.79)
May w/Dyn (0.98)
MustMay w/Dyn (0.95)
BMINSURF
DAER
DATR
DCHQ
DEDF
DODC
DSFD
DSSC
Fig. 5. Fortran results for a variety of static and/or dynamic activity analyses. May and
Must-May are static analyses and Dyn indicates dynamic activity analysis. Arithmetic
means are indicated within parentheses.
static/dynamic activity analysis may reduce the overhead of dynamic activity
checking. Since we are concentrating on forward mode AD, a must-useful vs.
may-useful analysis is not exploitable.
Using OpenAnalysis, we implemented the must-may activity analysis. We
designed a new set of sax routines that would skip the check of the activity
flag on the known must-may-active gradients. To avoid any extra checking in
this regard, we re-order the arguments to the sax calls to identify by position
the gradients that need to be dynamically checked and those that do not. We
manually adjusted the sax calls in each benchmark’s derivative code to comply
with the new interface. Then we used the must-may activity results to re-order
the arguments. We anticipate that this must-may activity analysis will become
an option in OpenAD, generating calls under the new interface and automatically
re-arranging the arguments.
5.2
Results
In Figure 5 we display the results of our hybrid static/dynamic activity analysis.
All data has been normalized to the execution time of No Activity Check. The
arithmetic mean per analysis run is noted in parentheses within the legend. The
second bar represents Pure Dynamic activity analysis and visually shows the
significant overhead (39% average) of dynamic activity checking. The third bar
represents the static May activity analysis with no dynamic activity analysis
and shows the advantage of pruning the derivative code at inactive variables
with an average speedup of 21%. The fourth bar represents the hybrid combination of the static may activity analysis with dynamic activity analysis. In most
benchmarks, the win from the static may analysis more than compensates for
the overhead of dynamic checking. The fifth bar represents the hybrid combination of the static Must-May activity analysis with dynamic activity analysis.
Three of the benchmarks show a decrease in execution time by using must-may
activity analysis rather than may activity analysis. We anticipate that as we
reduce the implementation overhead of our hybrid accumulation routines and
examine complex applications where more variables can be statically identified
as must-active, the benefits of our hybrid strategy will become more apparent.